冀北东猴顶A型花岗岩成因：岩石地球化学、锆石U-Pb年代学及Sr-Nd-Pb-Hf同位素制约  

Petrogenesis of the Donghouding A-typeGranite in Northern Hebei:Constraints from Geochemistry,Zircon U-Pb Dating and Sr—Nd—Pb—Hf Isotopic Composition

作　　者：梁清玲[1] 江思宏[2] 刘翼飞[2] 

机构地区：[1]四川省冶金地质勘查局六零六大队,成都611730 [2]中国地质科学院矿产资源研究所,北京100037

出　　处：《地质论评》2013年第6期1119-1130,共12页Geological Review

基　　金：国家自然科学基金资助项目(编号41030421、41273061);中国地质调查局地质大调查项目(编号1212011121074)的成果

摘　　要：本文对河北丰宁地区前人所定的东猴顶正长斑岩和石英正长斑岩进行了岩石学、锆石U-Pb年代学、元素地球化学以及Sr—Nd—Pb—Hf同位素分析。LA-MC-ICP-MS锆石U-Pb测年和岩石学显示东猴顶岩体为早白垩世(～129Ma)钾长花岗斑岩,而非前人认为的侏罗纪—白垩纪正长斑岩和石英正长斑岩。东猴顶岩体具有高硅(69.07%～73.00%)、富碱(Na2O+K2O:9.00%～10.56%)和FeO(全铁)/MgO比值大的特征,属高钾钙碱性系列;岩石富集轻稀土,负铕异常明显(δEu:0.25～0.41),相对富集K、Rb等大离子亲石元素和Zr、Hf、Th、U、Y等高场强元素,亏损Ca、Ba、Sr、P、Ti、Cr、Ni、Co等元素,Ga/Al比值高,具A型花岗岩特征,可能形成于伸展环境构造体制。岩体n(87Sr)/n(86Sr[)]i=0.70815～0.71197,εNd(t)值为-13.2～-16.8,对应的二阶段模式年龄(T2DM)为2.0～2.3Ga;全岩n(206Pb)/n(204Pb[)]i=16.745～16.765,n(207Pb)/n(204Pb[)]i=15.372～15.394,n(208Pb)/n(204Pb[)]i=37.706～37.794;锆石Hf同位素组成为εHf(t)值=-20.7～-9.2,二阶段模式年龄(T DM C)为1.9～2.6 Ga。同位素特征表明岩体源岩可能主要来自壳源物质。考虑到华北克拉通东部地壳生长的主要时期为新太古代,因此,东猴顶岩体的岩浆来源于太古代地壳物质和部分亏损地幔物质的混合源区,是华北克拉通北缘中生代岩石圈强烈减薄、地壳伸展作用的结果。This study presents bulk geochemical, Zircon U-Pb dating and Sr-Nd-Pb-Hf isotopic results for the Donghouding A-type granite in northern Hebei. LA-MC-ICP-MS zircon U-Pb dating results and petrological characteristics show that the Donghouding magmatic rock is the Early Cretaceous （ 129.3 - 129.5Ma） K-feldspar granite porphyry, not Jurassic-Cretaceous syenite porphyry and quartz syenite porphyry regarded by the former researchers. The Donghouding K-feldspar granite porphyry is High-K calc-alkaline, and characterized by high contents of SiO2=（72.15% - 73.00% ）, alkali （ Na2O＋ K2O：9.42% - 9.60% ）, and high FeO/MgO ratios. It is enriched in LREE and K, Rb, Zr, Hf, Th, U, Y, and depleted in Ca, Ba, Sr, P, Ti, Cr, Ni, Co, with negative Eu anomalies（δEu：0.25 -0.41） , high Ga/A1 ratios. The Donghouding K-feldspar granite porphyry is typical Atype granite, and may be formed in the extensional setting. The isotope （Sr-Nd-Pb-Hf） data of the Donghouding K-feldspar granite porphyry show the following characteristics： relatively high initial Sr [n（^87Sr）/n（^86Sr）]i =0.70815 -0.71197） , negative εNd（t） values （-13.2 ～ - 16.8） and the values of two-stage model ages （T2DM） ranging from 2.0 to 2.3 Ga; [n（^206pb）/n（^204pb）]i = 16.745～16.765, [n（^207pb）/n（^204Pb） ]i = 15.372 - 15.394, [n（^208apb）/n（=^204Pb） ]i = 37. 706 ～ 37.794; negative enf（t） values from -20.7 to-9.2 and the values of two-stage model ages（ TDMc） ranging from 1.9 to 2.6Ga. Although the Sr-Nd-Pb-Hf isotopic compositions suggest that the magma was sourced from Paleoproterozoic crust, the main growth period of eastern North China Craton crust is the Late Archean. Therefore, this paper concludes that the Donghouding K-feldspar granite porphyry was mainly derived from partial melting of Archean crust with some depleted mantle components. Geochronological and isotopic characteristics suggest that the Donghouding K-feldspar granite porphyry were the products of North China Craton li

关 键 词：A型花岗岩 锆石U-Pb年龄 岩石地球化学 Sr-Nd-Pb-Hf同位素 华北克拉通北缘 

分 类 号：P597[天文地球—地球化学]